1. Field of the Invention
The subject matter of the present invention generally relates to an agricultural harvesting machine with a crop picking head.
2. Related Technology
During harvest operations, agricultural harvesting machines of the present type are moved across a field to pick up or harvest plants by means of a crop picking head, transport them into the harvesting machine where the crop is processed, and finally transfer the processed plants or parts separated therefrom to a transport vehicle. As a rule, the crop picking head generally comprises one or more pickup conveyers which serve to pick up the plants from the soil. For example, prongs of a pickup attachment which pick up hay that has been mown in a previous operation and is ready to be picked up in a swath, or to separate the plants from the roots that remain in the soil and feed them into the crop picking head, such as the mowing and feeding-in drums of a corn picker head. A discharge conveyer receives the plants from the pickup conveyers and transfers them to a feed-in conveyer in the feed-in channel of the harvesting machine. Often, the discharge conveyers used are cross conveyer screws which additionally move the plants in the transverse direction relative to the center of the crop picking head. In other crop picking heads, the pickup conveyers are also responsible for the transverse movement which takes place on the front ends or rear ends in interaction with separate cross conveyer elements. So called cross conveyer drums can be used as pickup conveyers in the known crop picking heads.
The feed-in conveyer in the feed-in channel of the harvesting machine subsequently transports the plants to a harvested crop processing device of the harvesting machine, for example, a chopper drum, a threshing drum, or a threshing and separating rotor.
In a field chopper with a chopper drum, the speed of the feed-in conveyer (pre-press rolls) at a given rotating speed of the chopper drum determines the cutting length. To change the cutting length, the usual practice is to change the rotating speed of the feed-in conveyer of the field chopper, which can be implemented by change-over gears or adjustable, purely hydraulic drives or by a combination of mechanical and hydraulic drives. In such cases, the rotating speed of the chopper drum remains approximately constant so that the cutting length is inversely proportional to the rotating speed and speed of the pre-press rolls.
In some regions, a trend toward longer cutting lengths is presently observed. The longer cutting lengths require a relatively high speed of the feed-in conveyers of the field chopper. To avoid transport problems due to the difference in speeds during the transfer of the plants from the discharge conveyers of the machine to the feed-in conveyer of the field chopper, it is possible to drive all driven elements of the crop picking head at a higher rotating speed as well. For this purpose, multistage change-over gears are used. It has also been proposed that the crop picking head be driven at a speed proportional to the rotating speed of the feed-in conveyers. The disadvantage of varying the speeds of all driven elements of the crop picking head is that the rotating speeds of the pickup conveyers are increased as well, although such an increase does not improve the harvested crop transport and thus would not actually be necessary. It increases the drive power requirement, and, for example, in the case of a corn picker head with rotating mowing and feed-in drums, it leads to an increased rate of wear of the cutting knives and braking mechanisms of the crop picking head. Because of the higher rotating speeds which lead to higher centrifugal forces, corn cobs may be separated from the plants as well and thus be lost to the harvesting process.
WO 02/056672 A describes a harvesting machine with a crop picking head in which the discharge conveyers (i.e., the cross conveyer screw and the inclined conveyer drums) are driven at a speed which is independent of the speed of the pickup conveyers (pickup forks or mowing and feed-in assemblies). This is implemented in that the feed-in conveyer and the discharge conveyer together are driven by a first hydraulic motor while the pickup conveyer of the crop picking head is driven by a second hydraulic motor. The speed of the pickup conveyer depends on the forward speed of the harvesting machine.
This setup ensures that the speed of the discharge conveyer is firmly coupled to the speed of the feed-in conveyer so that at this point transfer problems are no longer to be expected. The speed of the pickup conveyer can be freely chosen and thus be adapted to the prevailing conditions. However, when the differences between the speeds of the two conveyers are too great, problems may arise during the transfer of the harvested crop from the pickup conveyer to the discharge conveyer. If, for example, at high forward speeds and long cutting lengths, the pickup conveyer moves considerably faster than the discharge conveyer, jams may occur at the receiving end in the area of the discharge conveyer. If, at low forward speeds and short cutting lengths, the pickup conveyer moves considerably more slowly than the discharge conveyer, the latter may tear up the harvested crop, which leads to non-uniform cutting lengths.
Another disadvantage of the setup described in WO 02/056672 A is that two mechanical drive connections must be disposed between the crop picking head and the harvesting machine. These drive connections must be attached and detached whenever the crop picking head is attached and detached. To overcome this problem, it has been proposed that a changeable speed-transforming gear unit be disposed between the pickup conveyer and the discharge conveyer. In this case, the change of speed of the feed-in conveyer is not automatically adjusted, instead, this adjustment of the speed transformation of the gear unit is made by the operator.